The present invention is in the general area of threaded closures and particularly relates to such closures for threaded containers for carbonated beverages.
The utilization of threaded closures for use in packaging of carbonated beverages has become very popular. The popularity is due in part to the fact that the consumer can open the package by merely unscrewing the closure from the container. No "bottle opening" tool is required. Another advantage is that the consumer is able to remove the closure, dispense part of the contents from the container and reclose the container by merely screwing the closure back thereon. Since the sealing system is generally of high fidelity, there will be little loss of carbonation and the remaining packaged product will be suitable for use at a later time.
Despite these advantages, the threaded container-closure package has potentially a serious problem, i.e., premature release of the closure from the container which can occur with great force. The premature release occurs as the user turns the closure to remove it from the container. As the closure is turned, it moves axially upwardly thus breaking the seal between the top of the closure and the top of the container. Upon loss of the seal, pressurized gas enters between the sidewall of the closure and the container. If the closure is removed faster than the gas is being vented from the container, at the time the closure disengages from the container thread the container closure may be propelled off with great force, thereby presenting danger to the consumer.
One of the most popular threaded closures used in packaging carbonated products is the nearly ubiquitous metal cap. To aid in preventing premature release of this type of closure the art has suggested providing a vent slot through the container threads. The slot provides a path for the pressurized gas to vent to the atmosphere. See U.S. Pat. No. 4,007,848. In U.S. Pat. No. 4,007,851, another venting method for metal closures is shown. The closure is constructed to have, at a point adjacent the intersection of the sidewall and the top wall, at least one vent through which the pressurized gas may pass. Another type of system, one which uses circumferential venting, is shown in U.S. Pat. No. 1,739,659.
In the case of thermoplastic closures, attention has also been devoted to the provision of venting grooves or systems of various configurations in order to release the pressurized gas during the time the closure is being removed from the container. Some of the developments along these lines are described for example in U.S. Pat. Nos. 3,888,347, 4,382,521, and 4,427,126.
In accordance with this invention, a new venting system for thermoplastic closures is provided. This venting system enables a relatively large volume of pressurized gas to be rapidly but safely vented as the closure is being unscrewed from the container but before the closure is disengaged from the container threads.